:^) The head was stuck on a spike, I think at Westminster, for some period of time, then taken down and given to Lady Raleigh, who kept it until her death (reportedly, and there's no particular reason to doubt the story). I'm sure it wasn't in the best of shape, although having drained out all the fluids would have been some help. Excarnation (pecked at by buzzards) would have been one problem, but hey, the guy was dead.
One month max or the yotes will twist off the wire.
Bailing wire is not strong enough and old barbed wire too brittle.